Magnetron oscillator



J. KuRsHAN Nov. l1,- 1952 MAGNETRON OSCIL.

Filed Nov. 2, 1949 ATOR . Snnentor Jerome Kurfazz Patented Nov. 11, 1952 MAGNETRON oscILLA'roR Jerome Kurshan, Princeton, N. J., assignorY to Radio Corporation of America, a corporation of Delaware Application November 2, 1949, Serial No. 125,094

Claims. 1

This invention relates to electron discharge devices and more particularly to vacuum tubes of the magnetron type suitable for generating oscillations at ultra-high frequencies.

In certain high frequency electron discharge devices utilizing a cathode which extends into a cavity resonator, the high frequency electric field of the resonator is such as to induce high frequency currents in the cathode. This condition is particularly manifest in conventional magnetron tubes of the interdigital type employing a single, quartervvave, cavity resonator sub-divided into a number of anode segments by means of rods or fingers alternate ones of which are mounted at one end on one end wall and are spaced axially from the opposite end Wall of the resonator at the other end and uniformly disposed around the cathode. Ths type of device is known as a single cavity, multi-segment magnetron.

In a copending application, Serial No. 695,512, filed September 7, 1946, now Patent No. 2,581,607, granted January 8, 1952, in the names of Carl I. Shulman and George R. Kilgore and assigned to the same assignee as the present application, it Was shown how this coupling of high frequency -energy to the cathode electrode may be enhanced and the cathode employed in a dual function to serve as the electron source and also as the output coupling element of the tube. While this means of energy transfer can be efiiciently used in various circuits, it is often desirable'to extract energy from the tube through afseparateelement independent of the cathode and its associated circuit. This is generally accomplished in the art by means of a simplecouplingflcop extending into the resontor. When such acoupling loop is to be used, or, generally speaking, when the coupling of energy is not being effected throughthe cathode, it is important to avoid any inherent coupling to the cathode.

Any unwanted cathode coupling results in a certain loss of energy and is considered in such cases a` defect or disadvantage.` Various means have been proposed to remedy this defect. However, in discharge devices utilizing a single cavity resonator these means have not been successful. In the multi-cavity type magnetron the construction inherently reduces cathode coupling to a negligible amount.

In accordance With the present invention, coupling of the high frequency fields to the cathode in an interdigital magnetron is substantially eliminated by extending the interdigital anode elements entirely through the resonator andy the construction ofthe tube is simplified by employing a stacked construction of alternate discs and washers or rings for the quarterwave resonator structure. The invention is applied to an interdigital magnetron having an even number of oppositely-disposed cavity resonators for neutralizing residual coupling to the cathode at each resonator.

Accordingly, the primary object of this invention is to provide improved means for eliminating high frequency energy transfer to the cathode in discharge devices utilizing cavity resonators.

Another object of the invention is to provide an improved multi-segment cavity resonator magnetron in which energy can be derived solely from an output coupling element independent of the cathode circuit.

.A further object of the invention is to provide a novel anode resonator structure involving a stacked construction of discs and washers or rings.

A feature of the invention is that the undesirable eiTect of coupling to the cathode is eliminated in a manner which entails no loss of high frequency energy and Without sacrifice of efciency.

A specic feature of the invention is the provision of a drum-shaped anode resonator, for an interdigital magnetron, having axially-apertured end plates connected by a ring or washer with an annular series of parallel anode rods, alternate ones of which are attached at one end to one plate adjacent the aperture therein and extendr` at the other end through recesses provided in the other plate adjacent its aperture, the other alter# nate rods being similarly arranged.

Another feature of the invention is the neutralization of residual coupling to the cathode circuit in a simple manner by means of a novel plural resonator structure.

Other objects and features will be apparent from the following description of the invention pointed out in particularity in the appended claims and taken in connection with the accompanying drawing in which: Y

Fig. l is a semi-schematic sectional view of a single-cavity magnetron having an anode resonator structure embodying my invention;

Fig. '2 is a front elevational view of a twocavity magnetron tube incorporating the invention with the housing partly cut away to show the constructional features of the elements;

Fig. 3 is a top plan view of Fig. 2 with the housing cut away along line 3-3 of Fig. 2;

Fig. 4 is a transverse sectional View taken along line 4--4 of Fig. 2;

Fig. 5 illustrates one side Wall of the resonator structure of |ligs. 2-4 looking parallel to the magnetic field; and

Fig. 6 is an enlarged perspective view of the dividing wall and the segments held thereby.

Fig. 1 shows a toroidal, quater wave cavity resonator 2 having a cylindrical cross-section and surrounding a central space 3. This resonator is made up-of two apertured discs or plates 'I spaced apart and connected by a cylindrical ring 8 as shown. The ring B may be a block or washer such as I9 or 20 inFigs. 2 4.

An elongated cathode 9 extends axially through the central space 3. This electrode 9 is preferably in the form of a tubular member housing a suitable lamentary heating element I9 which is connected to conductors I I and I2 in order to supply heating current to the filament. The cathode 9 is provided on its outer surface with suitable material to liberate electrons when heated to a certain temperature. plished by spraying the cathode with a coating of barium or strontium oxides, or other known substances, or the cathode may be made of an electron emitting substance. In any event, it is generally suicient to provide an electron emitthis, the apertures in the plates T are provided with radial projections and intermediate recesses, as shown in Fig. 5. The two plates `are oriented withthe projections on one plate registering with the recesses on the other plate, and vice-versa, andthe anode segments Iii are mounted at one end on the projections of one plate and extend at the other end through the recesses of the other plate: The segments I are similarly arranged between segments It.

It is intended to derive high frequency energy throughY an output coupling element independent of the cathode circuit. This may be accomplished in a conventional manner by means of an output coupling loop IS disposed within the resonator 2and connected to a coaxial output transmission line I'I, I8.

The anoderstructure of Fig. 1 is preferably constructed as follows. A sandwich, consisting of two suitably machined or punched discs for the end plates 'I and a cylindrical ring or bored block for the peripheral wall separating the discs, is assembled with the rods I4 and I5 in a jig. The jig consists of a base plate, suitablyV drilled to receive the anode rods and having upright aligningposts, and a cover plate drilled to receive the anode rods and the aligning posts. The jig is made of oxidized stainless steel which will not be wet by solder. The discs I and ring 8 are of silver plated copper. The rods are made from platinum-clad molybdenum wire for rigidity and ease of brazing. With the sandwich assembled with the rods in the jig the cover plate is bolted down and the entire assembly is sent through a hydrogen` furnace. At the proper temperature a silver-copper alloy forms which melts and brazes the parts together. After opening the jig the rods can be cut down to the desired length with ay cutting wheel.

In the operation of the device a magnetic eld is` essential and the pole pieces marked N and S This is generally accomiii) indicate in a schematic way that a magnetic fleld is provided parallel to the cathode 9. In practical applications this eld may be produced either by a permanent magnet or :an electro-magnet. These magnets are separate elements, not an integral part of the device, and consequently are not included in the various figures. Of course, it is understoodv that, for proper operation, a magnetic eld of a certain strength applied in the direction shown is necessary as well as an anode potential source between the resonator 2 and the cathode S, and a heating current source for the lament I0.

In the above-mentioned copending application it was explained how fringe elds created between resonator segments and walls produced an electric eld component parallel with the cathode or its associated conductors and thereby transferred energy to the cathode circuit. Examining Fig.` l, it will be seen that in my construction the gaps between the anode segments and the resonator walls face in directions normal to the cathode S, which markedly reduces the coupling tothe cathode.

Although the anode construction of Fig. 1 reduces the coupling of the high frequency-elds to the cathode to a minimum, there is some residual coupling due to axial component elds rihg'ing out from the gaps. solved in a copending application Serial No. 729,589, filed, February 19, 194.7,Y in the name of George R. Kilgore, and assigned to the same assignee as the present application,v `by providing means for dividing the resonator into two portions or resonators of opposite electrical fields and so arranging the anode segments in these resonators as to neutralize the: effect of the residual coupling. In the operation of such a discharge device, electrons under the influence of the magnetic field are caused to sweep segments in one resonator creating high frequency fringe fields in one direction and simultaneously to sweep segments in another resonator creating equal fringe fields in opposite direction and the coupling of these elds to the cathode is differentially combined, which results in zero effective coupling to the cathode.

Figs. 2 6, inclusive, illustrate my invention embodied in a two-cavity magnetron suggested in said Kilgore application. The peripheral walls of the two resonators 2A and 2B are formed by two juxtaposed, apertured, anode spacing blocks or washers I and 2n supported on a header 2I by means of studs 22. Each of the two apertured side walls or discs I at the opening in which the cathode 9 is located, are serrated toA form a plurality of spaced semi-circular cut-outs orY recesses 23 which provide clearance for the segments I4' supported by the dividing wall 'I". The projections 23 between the semi-circular recesses in walls?" provide supports for the alternate segments I5. The segments I4 are similarly sup ported by projections 23 on dividing wall I. The anode segments may be simple rods or bars and can be braced to their respective supports. This construction is illustrated particularly in Figs. 5 and 6.

The alternate walls 'i' of the two resonators constituting the anode are strapped together by the anode segments I5', in a manner somewhat analogous to the conventional strapping of alternateV resonator walls of multi-cavity magnetrons, although in the present case the required strap ping is in an axial direction.

Output loop I6' extends through lthe header 2I This problemv is Y and protrudes into the resonator 2B from a radial direction. One end of the wire loo-p IIB is connected to the anode block and the other end isV connected to conductor l1' which is sealed through a bead 24 on conductor I8. The cathode 9 is supported by the heater wires Il and I2' which are sealed through beads 25 on the header 2|. A cover 2B over the entire assembly and welded to the header 2| completes the structure and permits evacuation of the magnetron through 'an exhaust tabulation, not shown.

The anode structure of Figs. 2-6 is preferably constructed by an obvious extension of the technique described above for Fig. 1.

The magnetron device herein shown incorporates the invention by way of example in two different embodiments. Various modications will be apparent to those skilled in the art. Although two resonators are illustrated in Figs.

2-4, it will be understood that any even numternately connected at one end to one disc and extending at the other end through the other disc in spaced relation therewith.

2. A magnetron anode comprising a pair of parallel discs connected by a peripheral wall, wall means disposed between said discs and dividing the space bounded by said discs and wall into two adjacent cavity resonators, said discs and said wall means having aligned central apertures, and a series of parallel rods disposed around said apertures and connected to said wall means and extending through said discs in spaced relation therewith.

3. A magnetron anode according to claim 2, further including a second series of parallel rods connected to said discs between said rst-named rods and extending through said wall means in spaced relation therewith.

4. A magnetron anode comprising a plurality of parallel discs, having aligned apertures, a spacing member having an aperture of greater diameter than said disc apertures interposed between and joined to each pair of adjacent discs. each pair of adjacent discs and the spacing member therebetween' forming a cavity resonator, and parallel rods disposed around said disc apertures, alternate rods being connected to alternate discs and extending through an intermediate disc in spaced relation therewith, the other rods being connected to said intermediate disc and extending through said alternate discs in spaced relation therewith.

5. A strapped magnetron anode comprising apertured discs having their inner surfaces serrated and forming projectionawashers between said discs for producing a spacing between the latter.

and bars connected to the projections within alternate apertured discs only.

6. A magnetron anode comprising alternate stacked apertured discs and washers in electrically conducting relation forming quarter wave sections, and bars connected to alternate discs only.

7. A magnetron anode comprising a plurality of spaced, electrically connected, apertured discs. said discs being provided with spaced, internally extending projections, and bars connected to the projections in alternate discs only.

8. A magnetron anode comprising a plurality of stacked apertured discs and washers, and bars connected to alternate discs only and forming an interconnected interdigital segment assembly.

9. A magnetron having an anode comprising a pair of parallel discs having aligned apertures, a spacing member having an aperture of greater diameter than the disc apertures interposed between and joined to said discs, said discs forming a cavity resonator, and parallel rods disposed around said disc apertures and alternately connected at one endto one disc and extending at the other end through the other disc in spaced relation therewith, and an elongated cathode extending axially through said disc apertures, whereby during operating of said magnetron coupling to said cathode of high frequency iields generated between said rods and said discs is minimized.

10. A magnetron having an anode comprising a plurality of parallel discs having aligned apertures, a spacing member having an aperture of greater diameter than said disc apertures interposed between and joined to each pair of adjacent discs, each pair of adjacent discs and the spacing member therebetween forming a cavity resonator, and parallel rods disposed around said disc apertures, alternate rods being connected to alternate discs and extending through an intermediate disc in spaced relation therewith, the other rods being connected to said intermediate disc and extending through said alternate discs in spaced relation therewith, and an elongated cathode extending axially through said discs apertures, whereby during operation of said magnetron coupling to said cathode of high frequency iields generated between said rods and said discs is minimized at each cavity resonator and residual couplings at adjacent cavity resonators are neutralized.

JEROME KURSHAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,147,159 Grutton et al Feb. 14, 1939 2,428,888 Nelson Oct. 14, 1947 2,463,416 Nordsieck Mar. 1, 1949 2,505,529 Crawford et al. Apr. 25, 1950 

